I have tried the Sawyer and the Katadyn Be Free and much prefer the latter. When added to one of the (extremely good) HydraPak bottles - I have a 2 litre one - it forms a really functional water purification set-up. OK, with the Sawyer, you can use old soft drinks bottles, saving money, but the problem is filling them efficiently: their openings are too narrow for convenience. It is perhaps here that the Katadyn wins the day as both the Katadyn-supplied bottle and the HydraPak have wider openings, making filling significantly easier. That, and a better flow rate through the Be Free filter clinches the deal for me.
You might save money with the Sawyer system but, every time I head out, it's the Be Free + HydraPak combo that's in my rucksack.
These are merely observations from personal experience. As ever, I've absolutely no association with either company; I'm just a happy customer.